Asphalt mixes are commonly used as paving materials for road construction and maintenance. Typically, asphalt, often referred to as asphalt binder, asphalt cement or bitumen, is mixed with aggregate to form material used in asphalt paving. Processing and use of this material yields asphalt pavement. More particularly, asphalt pavement comprises aggregate held within a continuous phase of the asphalt binder by adherence of the asphalt binder to the aggregate.
The strength and durability of the asphalt pavement depends on various factors such as the properties of the materials used, the interaction of the various materials, the mix design, construction practices and environmental and traffic conditions to which the pavement is exposed. To produce a mix that will have good performance during the lifetime of the pavement, it is important to attain proper coating of the aggregate with the asphalt and good adhesion between both components, as well as good overall cohesive strength of the asphalt.
Conventional asphalt materials suffer from various types of distress modes due to exposure to environmental conditions, such as, for example, permanent deformation, creep and rutting at high temperatures and brittleness and cracking at low temperatures. To improve resistance of asphalt materials to these various distress modes, high temperature performance additives, e.g., plastomers and/or elastomers, and/or low temperature performance additives, e.g., process oils, are incorporated into the asphalt materials. The high temperature performance additives tend to increase the modulus of the asphalt material at higher temperatures to resist permanent deformation and creep while the low temperature performance additives tend to increase flexibility and ductility of the asphalt material at lower temperatures to resist brittleness and cracking.
Unfortunately, current low temperature performance additives are not always as effective as desired at increasing the flexibility and ductility of the asphalt material at lower temperatures, and often detract from the high temperature performance properties of the asphalt material even with the addition of high temperature performance additives. On the other hand, current high temperature performance additives are not always as effective as desired at reducing permanent deformation, creep and rutting at high temperatures, and often detract from the low temperature performance properties of the asphalt material even with the addition of low temperature performance additives. Typical polymers used to modify asphalt binders to reduce or prevent rutting include elastomers, such as, for example, styrene/butadiene/styrene copolymer (SBS), and plastomers, such as, for example, polyethylene, ethyl/vinyl acetate copolymer (EVA), and the like.
The asphalt Performance Grade (PG) rating system categorizes asphalt binders used in asphalt pavement based on the binder's performance at different temperatures. An asphalt binder having a PG rating of about 64-22, for example, means that the asphalt binder can be used in a climate where the pavement reaches temperatures as high as +64° C. and as low as −22° C. Temperatures outside the PG range of the asphalt binder usually lead to deterioration of the asphalt pavement in which this binder is used. Hence, it has for some time been an objective to broaden the PG range of asphalt binders used in road pavement applications.
The Useful Temperature Interval (UTI) of an asphalt is the difference between the high and low temperature PG grading. Generally, to obtain a UTI of >92° C., a modified asphalt is needed. For example, PG 76-22, a common polymer modified asphalt, has a UTI of 98° C. In addition to increasing the PG range of the asphalt binder, modifiers also improve other qualities of the resulting asphalt, such as its general toughness and wear characteristics.
There remains a need for new asphalt binder modifiers that broaden the PG range and increase the useful temperature interval of asphalt binders. Other desirable features and characteristics of the asphalt binder compositions and methods of making and using same that are described herein will become apparent from the following detailed description and the appended claims.